The state of the art in biomimetics

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The state of the art in biomimetics
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2013 Bioinspir. Biomim. 8 013001
(http://iopscience.iop.org/1748-3190/8/1/013001)
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UBLISHING
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IOINSPIRATION
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IOMIMETICS
Bioinspir.Biomim.8 (2013) 013001 (11pp)
doi:10.1088/1748-3182/8/1/013001
PERSPECTIVE
The state of the art in biomimetics
Nathan F Lepora
1
,Paul Verschure
2
and Tony J Prescott
1
1
Sheffield Centre for Robotics,University of Sheffield,UK
2
Synthetic Perceptive,Emotive and Cognitive Systems (SPECS),Institucio Catalana de Recerca i
Estudis Avancats,Universitat Pompeu Fabra,Barcelona,Spain
E-mail:n.lepora@sheffield.ac.uk
Received 17 August 2012
Accepted for publication 3 December 2012
Published 9 January 2013
Online at stacks.iop.org/BB/8/013001
Abstract
Biomimetics is a research field that is achieving particular prominence through an explosion of
new discoveries in biology and engineering.The field concerns novel technologies developed
through the transfer of function frombiological systems.To analyze the impact of this field
within engineering and related sciences,we compiled an extensive database of publications for
study with network-based information analysis techniques.Criteria included publications by
year and journal or conference,and subject areas judged by popular and common terms in
titles.Our results reveal that this research area has expanded rapidly fromless than 100 papers
per year in the 1990s to several thousand papers per year in the first decade of this century.
Moreover,this research is having impact across a variety of research themes,spanning
robotics,computer science and bioengineering.In consequence,biomimetics is becoming a
leading paradigmfor the development of new technologies that will potentially lead to
significant scientific,societal and economic impact in the near future.
(Some figures may appear in colour only in the online journal)
1.Introduction
Biomimetics is the development of novel technologies through
the distillation of principles from the study of biological
systems.Biomimetic technologies arise from a flow of ideas
from the biological sciences into engineering,benefiting
from the millions of years of design effort performed by
natural selection in living systems (Bar-Cohen 2006a,Allen
2010).This transfer of function from the natural world to
artificial devices has driven novel research agenda across many
disparate disciplines,from materials science and architecture
to computer science and robotics.More recently,advances
in robotics have facilitated the development of biomimetic
robotics inspired by the different design plans found in
the animal kingdom (examples shown in figure 1).Such
biomimetic artifacts can provide excellent models of their
biological counterparts,allowing us to ask and answer
questions about the biological systemthat cannot be addressed
through experiments alone.We emphasize that it is the
transfer of function from biology to the machine that allows
biomimetics to test hypotheses from the biological sciences;
otherwise,there is a danger of merely blind copying or
mimicry of design principles with no further insight into
the living system.In this sense of transferring biological
function,biomimetic systems can thus provide a test bed
for theoretical ideas in biology and a means for generating
biological solutions to challenges in science and technology,
and we may consider them an implementation of ‘living
machines’.
Over the last decade,there has been an explosion
of important discoveries within the many research topics
comprising biomimetics.The societal and economic impacts
expected to emerge from these advances will have future
benefits for our health and quality-of-life,due to advances
in information and computation technologies,robotics,
brain–machine interfacing and nanotechnology applied to
life sciences.Given this potential of biomimetics,many
international funding initiatives are underway to drive the
field forward.However,for the field to fully realize its
potential,it is necessary to have information gathering and
coordination initiatives that can inform policy makers about
1748-3182/13/013001+11$33.00
1
©2013 IOP Publishing Ltd Printed in the UK &the USA
Bioinspir.Biomim.8 (2013) 013001 Perspective
(A)
(D) (E)
(B)
(F)
(C)
Figure 1.Examples of biomimetic robots.(A) Stickybot:Gecko-inspired climbing-robot developed at Stanford University (Kimet al 2008,
photo credit:Mark Cutkosky).(B) Robobee:Insect-like micro-air vehicle fromthe Harvard Microrobotics Lab (Sreetharan et al 2012,photo
credit:The Harvard Microrobotics Lab).(C) Shrewbot:rodent-like,whiskered robot developed by Bristol Robotics Laboratory (Prescott
et al 2009,Sullivan et al 2012,photo credit:Ben Mitchinson).(D) Robotic octopus tentacle:developed at the University of Pisa,Italy
(Mazzolai et al 2012,photo credit:Cecilia Laschi).(E) iCub:a child-like humanoid robot developed at the Italian Institute of Technology
(Metta et al 2008,photo credit:Lorenzo Natale).(F) Robot lobster:developed at North-Eastern University (Ayers et al 2011,photo credit:
Daniel Blustein).
appropriate strategic decisions.A recent initiative toward
this goal in the European research area is the Convergent
Science Network (CSN) of biomimetic and biohybrid
systems (http://csnetwork.eu),which facilitates surveying and
road-mapping exercises combined with other coordination
actions for bringing researchers in the field together.Activities
include organizing Living Machines:The First International
Conference on Biomimetic and Biohybrid Systems (Prescott
et al 2012),from which selected papers will be published in
Bioinspiration and Biomimetics.
This work is a survey of the state of the art of biomimetics
based on an information analysis of a comprehensive database
of publications on biomimetics in engineering and related
sciences.While there are already many excellent reviews of
biomimetics (Bar-Cohen 2006b,Vincent et al 2006,Barthelat
2007,Teeri et al 2007,Pfeifer et al 2007,Fratzl 2007,Bhushan
2009,Bongard 2009,Helms et al 2009,Gebeshuber et al
2009,Johnson et al 2009,Wilson et al 2010,Nagel and Stone
2011,Nosonovsky and Rohatgi 2012,Rawlings et al 2012),
such accounts usually emphasize subjects that are part of the
authors’ expertise and research priorities.Instead,our aimis to
provide a complementarysurveytothese existingreviews from
the viewpoint of a more objective statistical survey across the
field of biomimetics in engineering and related sciences.In
particular,we focus on the following four main questions.
Where is biomimetic research published?How rapidly is
the subject of biomimetics expanding?What subjects does
biomimetics encompass?And are there research communities
within biomimetics?By focusing on these questions,our
intention is that the answers will clarify the current state of
the fields comprising biomimetic research,how these fields
evolved to their present state,and where they appear to be
heading in the future.
2.Background to biomimetics
Biomimetics can,in principle,extend to all fields of
biological research from physiology and molecular biology
to ecology and from zoology to botany.Promising
research areas include system design and structure,self-
organization and co-operativity,new biologically active
materials,self-assembly and self-repair,learning,memory,
control architectures and self-regulation,movement and
locomotion,sensory systems,perception,and communication.
Biomimetic research,particularly at the nano-scale,should
also lead to important advances in component miniaturization,
self-configuration and energy efficiency.Another key focus
is on complete behaving systems in the form of biomimetic
robots that can operate on different substrates in a sea,
on the land,or in the air.A further central theme is the
physiological basis for intelligent behavior as exploredthrough
neuromimetics—the modeling of neural systems.Exciting
emerging topics within this field include the embodiment of
neuromimetic controllers in hardware,termed neuromorphics,
and within the control architectures of robots,sometimes
termed neurorobotics.
Historically,the term ‘biomimetics’ was first used
by Otto Schmitt during the 1950s,when he made a
2
Bioinspir.Biomim.8 (2013) 013001 Perspective
distinction between an engineering/physics approach to the
biological sciences,which was termed ‘biophysics’,and
a biological approach to engineering,which he termed
biomimetics.Schmitt is also credited with establishing the
field of biomedical engineering,which now encompasses the
important discipline of biomaterials that retains its strong
connections tobiomimetics.Arelatedtermusedinengineering
is ‘bionics’,which was introduced by Jack Steel of the US
Air force to mean copying and taking ideas from nature
(popularized in Daniel Halacy’s book Bionics:The Science
of Living Machines (Halacy 1965)).Another term that is
now commonly used is bioinspired or biologically inspired,
such as in the modern discipline of biologically inspired
computing.Bioinspired computing tends to focus on bottom-
up,decentralized approaches to computation,such as genetic
algorithms,in contrast with the more traditional top-down
approach of artificial intelligence.Terms such as neuro-
based and brain-based are now also being used,where the
emphasis is more specifically based on the central nervous
systemof animals.
3.An information analysis methodology
To strive to be as objective as possible with this work,we
adopted a methodology in which the state of the art was
surveyed using techniques from information analysis.An
important aspect of this type of analysis of large datasets is
howthe results are visualized.Friedman (2008) stated that the
‘main goal of data visualization is to communicate information
clearly and effectively through graphical means....To convey
ideas effectively,both aesthetic form and functionality need
to go hand in hand...’.Accordingly,we used a variety of
traditional and modern visualization techniques,including pie
charts,word clouds and connected graphs,to give a range of
perspectives on the implications of the analysis.
Our general strategy was to construct a comprehensive
database of publications on biomimetic research in
engineering and related sciences,using general web-based
resources for journals and conferences,such as IEEE
Xplore,Elsevier’s Scopus and the Thomson Reuters Web of
Knowledge.A range of synonyms for biomimetics were used
as search terms,including biomimetics,biomimetic,bionics,
bionic,biomimicry,bioinspired and bioinspiration.The focus
of this study was specifically on biomimetics in engineering
and related disciplines,and hence we narrowed the search
to include only papers in engineering,physics,mathematics,
robotics,computer science and related disciplines.The
resulting database was then analyzed to infer the general
breakdown of the field,e.g.,by year,journal or conference,
and subject areas are judged by common words in titles.
The implementational details of this methodology are
given in two appendices:database construction in appendix A
and database analysis in appendix B.In particular,we describe
how the information was extracted from the online databases
in a formthat could then be analyzed froma standard desktop
personal computer.Intotal,we extractedapproximately18000
publications on biomimetic research covering the years 1995–
2011.Our analyses consisted of a series of tests,including
the analysis of year and journal or conference in which they
were published;a survey of biomimetic publications by topic
based on the most frequent terms in the titles of papers;and
then an analysis of community structure within the connected
network of papers linked by pairs of words in the titles that are
common.
We emphasize from the outset that there are two main
limitations of this information analysis approach.First,papers
not clearly labeled as biomimetic research,by their title or
otherwise,were not included in our database,even though their
content might be considered as clearly biomimetic.Second,
papers may be incorrectly labeled as being biomimetic even
though their subject matter is not.These are unavoidable
limitations of the information analysis tools and database
information that are currently available.As such,the approach
adopted here identifies those papers that have been labeled as
biomimetic by their authors,and we assume that the results
obtained on this dataset are the representative of biomimetics
as a research field.
4.Where is biomimetic research published?
The first question is:In which journals and conferences
biomimetic research is published?We then considered
secondary queries,such as the impact of the journals and the
proportion that biomimetics comprises of the total published
content.
From a total of about 18 000 biomimetic publications in
the database,close to 10 300 (57%) were published in journals
and 7700 (43%) in conference proceedings.Altogether,1925
distinct journals and 1543 distinct conferences had at least
one publication on biomimetics.The 57% to 43% overall
split for journals to conferences in comparison with an
approximate split of 11% to 89% for papers from just the
IEEE Xplore database,63% to 38% for papers from Scopus
and 89% to 11% for papers from the Web of Knowledge.
Based on these statistics,biomimetics overall has a higher
proportion of research published in journals than conferences.
However,there are considerable differences betweendatabases
due to differences in coverage.In particular,the IEEE
database favors engineering and robotics and thus contains
more biomimetics papers fromconferences,consistent with a
culture of dissemination through conference publications on
those subjects.
The 12 leading journals in biomimetics ordered by the
total number of publications are visually displayed with a
pie chart (figure 2(A)),with only journals having more than
100 publications in biomimetics shown in the figure.Further
details of the leading journals are given in table 1,including
the journal abbreviation (to interpret the labeling in figure 2),
publisher,2011 impact factor and biomimetic publication in
2011 compared to the total journal output.The top five journals
in order of publication number are:Biomaterials (Elsevier)
with a total of 484 papers,followed by Bioinspiration and
Biomimetics (IOP) with 343 papers,the Journal of Biomedical
Materials Research A (Wiley) with 228 papers,Langmuir
(ACS) with 164 papers and Acta Biomateriala (Elsevier) with
159 papers.The content of these journals are split over general
3
Bioinspir.Biomim.8 (2013) 013001 Perspective
Figure 2.Journals and conferences publishing research on biomimetics.The pie charts represent the proportion of papers on biomimetics
published in the leading journals and conferences ranked by the total number of publications.A total of close to 10 300 biomimetic
publications in journals and 7700 in conferences were considered.The legend gives abbreviations for these journals and conferences,with a
key for the complete names given in tables 1 and 2.
Table 1.Leading journals publishing research on biomimetics.Journals are taken fromthe chart on left in figure 2 and represent the leading
journals ranked by the total number of research papers on biomimetics.The journals listed in this table were selected by having more than
100 publications in biomimetics.The abbreviations used in the key in figure 2 are given with the full journal name.The publisher,2011
impact factor,number of papers in biomimetics in 2011 and total number for 2011 are also given.
Impact Papers
Abbreviation Journal Publisher (2011) (2011)
BIOMATERIALS Biomaterials Elsevier 7.4 55/1007
BIOINSPIR BIOMIM Bioinspiration and Biomimetics IOP 2.0 89/89
J BIOMED MATER RES A Journal of Biomedical Materials Research A Wiley 2.6 18/270
LANGMUIR Langmuir ACS 4.1 48/1936
ACTA BIOMATER Acta Biomaterialia Elsevier 4.9 27/454
J MATER SCI Journal of Materials Science:Materials in Medicine Elsevier 2.3 18/285
J BIONIC ENG Journal of Bionic Engineering Elsevier 1.0 25/52
ADVANCED MATERIALS Advanced Materials Wiley 13.9 27/789
NATURE Nature NPG 36.0 20/841
BIOPHYS J Biophysical Journal Cell 3.7 6/696
BIOMED MATER Biomedical Materials IOP 2.1 27/170
IEEE T SYST MAN CY IEEE Transactions on Systems,Man and Cybernetics IEEE 2.1 7/109
biomimetics and materials science in medicine.At present
Bioinspiration and Biomimetics is publishing the maximum
number of papers on biomimetics per year,followed by
Biomaterials and then Langmuir.
The six leading conferences that cover biomimetics are
displayed in a pie chart (figure 2(B)),which were selected
according to those with more than 100 publications in
biomimetics.Further details are given in table 2,including
the journal abbreviation and the number of biomimetic
publications in 2011 compared with the total number
of publications that year.The top three conferences in
biomimetics are:Robotics and Biomimetics (ROBIO) with a
total of 2796 papers,the International Society for Photonics
and Optics (SPIE) with 415 papers and the International
Conference on Automation and Logistics (ICAL) with 201
papers.Clearly,ROBIO dominates the research output on
biomimetics published in conferences,giving around one-
third of all conference papers on the robotic aspects of
biomimetics.In addition,ICRA and IROS also focus on
robotics,particularly automation and intelligent systems,and
are regarded as leading conferences on robotics with highly
competitive publication requirements.Five of the six leading
conferences are sponsored by IEEE,which indicates the
emphasis of these applications of biomimetics in relation to
engineering and technology.
5.How rapidly is the subject of biomimetics
expanding?
Our next question concerns:How rapidly biomimetics is
expanding as a subject area?From counting the number of
publications each year in our database,we see that in the first
decade of this century there has been an explosive growth
in biomimetic research,with the number of published papers
each annumdoubling every 2–3 years (figures 3 and 4).From
a relatively small field in the mid-1990s of less than 100 papers
per year,biomimetics has exponentially expanded thereafter
to reach critical mass of several hundred papers per year by
4
Bioinspir.Biomim.8 (2013) 013001 Perspective
Figure 3.Growth of biomimetic journals and conferences.The plots shows the number of papers published each year in biomimetics for the
leading journals (left panel) and conferences (right panel) starting from1995.The legend gives abbreviations for these journals and
conferences,with a key for the complete names given in tables 1 and 2.
Table 2.Leading conferences in which research on biomimetics is
published.Conferences are taken fromthe right-hand side of the
chart in figure 2 and are ranked according to the total number of
publications on biomimetics.The conferences listed in this table
were selected by having more than 100 publications in biomimetics.
The abbreviations used in the key in figure 2 are given with the full
conference name.The number of papers or abstracts in biomimetics
published in 2011 is also given with the total for the conference.
Abstracts and
Abbreviation Conference papers (2011)
ROBIO Robotics and Biomimetics 536/536
SPIE International Society for 62/2800
Photonics and Optics
ICAL International Conference 42/107
on Automation and Logistics
EMBC Engineering in Medicine 23/2100
and Biology Conference
ICRA International Conference on 19/1032
Robotics and Automation
IROS Intelligent Robots and 8/719
Systems
2002,a mature field with more than 1000 publications per
year by 2005,and currently has close to 3000 publication per
year.Over the last 15 years,this growth has far outpaced that
across science in general,which averages close to 6% per
year (doubling every 13 years) (Larsen and von Ins 2010).
Furthermore,the rapid growth in biomimetics has not yet
saturated,so this expansion compared to science as a whole is
expected to continue in the near future.
Based on this analysis,there is a boom in bioinspired
research.Leading discoveries in biomimetics have laid the
foundations for large areas of present and future research
works.This changing research landscape should lead to
changes in the composition of academic departments.We
expect that a greater number of researchers,research groups
Figure 4.Growth of biomimetic research.The bar chart plots the
number of papers published each year in biomimetics starting from
1995.The black bars indicate the proportion of journal papers and
the white bars indicate the proportion in books and conferences.
and departments in leading universities will be explicitly
focused around biomimetic research.This is consistent with
the range of biomimetic research groups belonging to the
subscribers of the Convergent Science Networkof biomimetics
and biohybrid systems (http://csnetwork.eu/members_list).
This expansion in biomimetic research and technological
development is also reflected in the increased numbers
of publications within individual journals and conferences
(figure 3).In some cases,this has been from the publication
5
Bioinspir.Biomim.8 (2013) 013001 Perspective
Figure 5.Popular topics in biomimetics.The word cloud shows the popularity of terms occurring in the titles of papers on biomimetic
research.The word size is proportional to the frequency of word occurrence.
of new journals and conferences in biomimetics that have
since flourished,in particular the journal Biomimetics and
Bioinspiration (2006) and the conference proceedings for
ROBIO (2004).In other cases,this expansion has related to
a change of focus of journals and conferences that have been
established for many years,such as the journal Biomaterials
(1980),and the conferences ICRA (1984) and IROS (1988).
The rapid expansion of ROBIO as a conference is clearly
evident in figure 3,compared with a more modest but still
appreciable expansion of the other conferences.
As these developments in robotics and engineering
are translated into technology,they have the potential for
significant societal and economic impacts.The growth of
technological transfer is seen from a corresponding rise
in patents granted in biomimetics (Bonser 2006,Bonser
and Vincent 2007).By a similar procedure to the present
analysis of academic publications,Bonser searched the US
Patent and Trademark Office (USPTO) from 1985 to 2005
for the keywords ‘biomimetic’,‘bionic’,or ‘biologically
inspired’.He then found that the cumulative number of
patents approximated the leading half of a sigmoid distribution
(Bonser 2006,figure 1).That being said,we would comment
that even though his data clearly showa remarkable growth in
patents on biomimetics (of about 100 per year in 2005),there
is little evidence for the claimed saturation fromthe presented
data.He then continued his arguments with the claimthat since
patents secure the legal right to exploit an invention but are
expensive to prepare,the very act of patenting an invention
indicates that the inventor has some confidence that a product
has fair chance to be brought to market.Hence,Bonser’s patent
study indicates that rapid development of new technologies
derived frombiological models is taking place.
6.What subjects does biomimetics encompass?
The next questionfor analysis is:What are the individual topics
that make up biomimetic research,and how do they vary in
popularity?To answer this question,we gave a simple pictorial
representation of these subject areas in a word cloud (figure 5),
accompanied by the statistics for the 100 most common topics
(summarized in table 3).
Word clouds,and data clouds more generally,are a visual
depiction of the frequency of words within a larger set obtained
by scaling the font size of each word within the cloud by its
frequency of occurrence.The clouds used in this work place
the words randomly,with the overall layout determined mainly
by aesthetics and readability.Technical details of howthe word
clouds were constructed are described in appendix B for the
database analysis,although we note here that common but
uninformative terms such as parts of speech were excluded
fromthis analysis.Note that since the area of word scales with
the square of its font size,word clouds tend to emphasize the
most common words while filtering out those words that are
less frequent.
Given that the database was constructed from papers
concerned with biomimetics,it is expected that many of
the leading concepts in the word cloud (figure 5) relate
directly to the overall subject area of biomimetics and its
synonyms such as bionic and bioinspired.Furthermore,words
indicating the biomimetic research process are also popular,
suchas ‘based’,‘model’ and‘design’.Overall,the secondmost
popular concept for this database is ‘robot’.This indicates that
much of contemporary biomimetic research published in the
Engineering journals is focused on applications in robotics,
as reinforced by ‘control’ being another popular term.Our
interpretation of this robot–control pairing of concepts is that
the control of robots is a problem as important as designing
and building the hardware itself.Indeed,in many ways,there
have been huge advances in building robots due to progress in
microcomputer-based technology.However,the utilization of
these sophisticated devices lags behind the effortlessly smooth
control displayed by apparently primitive insects or infant
animals.The fact that control is a key concept in biomimetics
indicates that a main research topic is to take inspiration from
how animals control their bodies and sensory systems.
Other,less common,topics fromthe word cloud indicate
a wide variety of research taking place in biomimetics.
A broad variety of research topics is directly inspired
by nature,including polymers,composites,fish,muscle,
collagen and vision.Some terms are taken directly from
biomedical research,such as bone,tissue and cell,reflecting
the large impact of biomimetics upon this research area.This
6
Bioinspir.Biomim.8 (2013) 013001 Perspective
Table 3.Top 100 most common topics in biomimetics.Topics are taken fromthe titles in a database of around 18 000 publications on
biomimetics.
Word Frequency(%) Word Frequency(%) Word Frequency(%) Word Frequency(%)
Biomimetic 17.5 Composite 2.7 Fish 1.7 Active 1.2
Robot 13.0 Development 2.7 Mobile 1.6 Collagen 1.2
Based 11.6 Bone 2.6 Optimization 1.6 Assembly 1.2
Model 7.5 Novel 2.6 Effect 1.6 Vision 1.2
Design 6.8 Materials 2.4 Simulation 1.6 Underwater 1.2
Control 6.7 New 2.3 Learning 1.5 Membranes 1.1
Bionic 5.7 Synthesis 2.2 High 1.5 Acid 1.1
Inspired 4.1 Method 2.2 Mechanical 1.5 Behavior 1.1
Application 3.9 Approach 2.2 Characterization 1.5 Peptide 1.1
Human 3.8 Bioinspired 2.1 Formation 1.5 Nano 1.1
Analysis 3.5 Research 2.1 Detection 1.5 Vitro 1.1
Study 3.4 Properties 2.0 Fabrication 1.4 Force 1.1
Engineering 3.3 Neural 2.0 Hydroxyapatite 1.4 Scaffold 1.1
Sensor 3.2 Like 1.9 Vehicle 1.4 Technology 1.1
Tissue 3.2 Protein 1.9 Calcium 1.4 Planning 1.0
Structure 3.1 Motion 1.9 Adhesion 1.3 Experimental 1.0
Polymer 3.0 Recognition 1.9 Hybrid 1.3 Environment 1.0
Artificial 3.0 Actuator 1.8 Molecular 1.3 Pattern 1.0
Surface 2.9 Cells 1.8 Performance 1.3 Effects 1.0
Self 2.8 Mechanism 1.8 Poly 1.3 Phosphate 1.0
Network 2.7 Surfaces 1.8 Muscle 1.3 Processing 1.0
Algorithm 2.7 Multi 1.8 Apatite 1.3 Visual 1.0
Bio 2.7 Micro 1.7 Membrane 1.2 3d 1.0
Cell 2.7 Dynamic 1.7 Time 1.2 Structural 1.0
Biological 2.7 Scaffolds 1.7 Adaptive 1.2 Information 1.0
emphasis on biomedical research is consistent with the journal
Biomaterials and Biomedical Materials Research having
leading publications for biomimetic research.In addition,
concepts from control engineering and artificial intelligence
are also represented,including model,network,algorithm,
simulation,learning,adaptive and optimization.These subject
areas are consistent with biomimetics being published in
robotics and engineering journals and conferences,such as the
journal IEEE Transactions on Systems,Man and Cybernetics
and the conferences ROBIO,IROS and ICRA.
7.Are there research communities within
biomimetics?
Our final questions are concerned with the topography and
inter-connectedness of biomimetics as a research field.A
specific point of interest is whether the field of biomimetics
functions as a coherent whole or fractures into distinct fields
with little connection between disparate areas.We comment
that there have been several academic networks concerned
with biomimetics,many of which have had a specific interest
area.However,it is not clear that these endeavors have caused
biomimetics to fracture into separate disciplines,in that they
individually title their work based on a biomimetic sub-
discipline to which they belong.To determine if there are
sub-disciplines of biomimetics and what these are,we instead
consider a network analysis of common nomenclature in the
titles of papers.
To address these questions,we use techniques from
network theory to analyze the connectedness of biomimetic
research.We begin with the most frequent topics in
biomimetics that were discussed in the previous section and
displayed in figure 5.We then quantify the connectedness
between pairs of topics by their co-occurrence within
publication titles,defined from a statistical measure of their
tendency to pair together relative to their chance level of
randomco-occurrence (appendix B).Interpreting the frequent
biomimetic terms as nodes on a graph,this co-occurrence
measure defines the strength of the connections between these
nodes.The results of such an analysis are displayed in figure 6,
with the thickness of the connections proportional to the co-
occurrence measure between topic pairs and the size of the
topic words proportional to their frequency (as in figure 5).
The positioning and color of the connections and nodes are
related to further analysis that we describe below.
For ease of interpretation,the top 50 word pairs are also
shown in table 4.Some of these word pairs are from phrases
such as ‘three dimensional’,which are not informative about
howresearch areas are related but do serve to bind such terms
together for interconnection with other terms.Other word
pairs are more informative about how areas of research are
related.For example,‘flapping’ with ‘wing’ indicates that
inspiration from biology is the key theme for flying robots,
while ‘underwater’ with ‘vehicle’ indicates an application of
biomimetic robotics.
Related terms can then be positioned together by the
use of network analysis,for which we used the Gephi
visualization software and toolkit (Bastian et al 2009).First,
we applied the Force Atlas algorithm,which pulls together
strongly connected nodes while repelling all other nodes
(further details in appendix B).In consequence,terms that
tend to occur together are positioned closely on the graph
while words that infrequently co-occur are positioned further
apart.This positioning is shown in figure 6.The next stage
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Bioinspir.Biomim.8 (2013) 013001 Perspective
Figure 6.Connectedness of popular terms in biomimetics.Two words in the word cloud in figure 5 are considered connected if they
co-occur within the same titles,with the co-occurrence frequency giving the connection strength.A Force Atlas algorithmwas applied to
these node words and connection strengths,which pulls together the connected terms.The graph is colored according to a modularity
analysis,which finds communities within the connected network,where a community is defined to be a group of nodes that have denser
intra-connections but sparser connections with other communities.
of the investigation used a modularity analysis to looks for
communities that tend to group together within the network.
This modularity analysis results in a modularity score of 0.4,
which is greater than the threshold of 0.3 usually taken to
indicate community structure.This result implies that there
are distinct communities,or groups of terms that are more
densely connected together within their community than to
the other communities.
Five communities are evident from the modularity
analysis,which are denoted with the distinct colors in
figure 6.Our interpretation of these communities are that they
are related to the following.(1) Robotics (blue)—covering
traditional robotics with an emphasis on having control and
intelligent,autonomous operation that is based on biology;
applications include computer vision,walking robots and
manipulators;methods include pattern recognition,neural
networks,and other areas of machine learning.(2) Ethology-
based robotics (green)—with the emphasis on constructing
robot hardware based on animals;examples include flying
robots based on insects and birds,and underwater robots based
on fish.(3) Biomimetic actuators (yellow)—in particular,
artificial muscle and its underlying technologies in material
science.(4) Biomaterials science (red)—with an emphasis on
biological materials such as bone,tissue and collagen,and
their assembly and fabrication.(5) Structural bioengineering
(black)—with the emphasis more concerned with the micro-
structure of the biological materials.
Therefore,overall biomimetics as subject area is fairly
well inter-connected,indicating that it may be considered as a
single discipline.Within this connectivity,the field does form
distinct communities,as was confirmed by observing that each
community has a recognizable theme.
8.Summary of main results
By applying an information analysis to a comprehensive
database of publications on biomimetics over the last 15 years,
we could answer a set of strategic questions about the past,
present and future of the research field.
First,where biomimetic research is published?From
a total of nearly 18 000 biomimetic publications,about
57% were published in journals and 43% in conference
proceedings (figure 2).Across the databases,there was a
large variation in these proportions,with the IEEE database
8
Bioinspir.Biomim.8 (2013) 013001 Perspective
Table 4.Top 50 most common word pairs in biomimetics.Words are taken fromthe titles in a database of around 18 000 publications on
biomimetics,and the pairings measured by the frequency of co-occurrence relative to chance.
Word A Word B Co-occurrence measure Word A Word B Co-occurrence measure
Three Dimensional 72 Fin Fish 17
Real Time 68 Investigation Experimental 16
Flapping Wing 64 Insect Wing 16
Phosphate Calcium 55 Autonomous Underwater 16
Fluid Body 36 Assembly Self 16
Stem Cells 33 Muscle Artificial 16
Assembled Self 32 Mechanical Properties 16
Underwater Vehicle 29 Preparation Characterization 15
Lipid Membranes 29 Image Processing 15
Acid Poly 29 Bio Inspired 15
Pattern Recognition 29 Robust Controller 15
Power Low 29 Engineered Tissue 15
Transfer Energy 26 Between Interaction 15
Insect Flapping 25 Titanium Phosphate 15
Coating Titanium 25 Metal Polymer 15
Controller Fuzzy 24 Wing Vehicle 15
Parallel Manipulator 23 Machine Interface 15
Neural Network 20 Fin Underwater 14
Flapping Vehicle 20 Mimetic Bio 14
Coatings Phosphate 19 Navigation Mobile 14
Flexible Fin 19 Localization Mobile 14
Tissue Engineering 19 Porous Scaffolds 13
Autonomous Vehicle 18 Stem Cell 13
Metal Composite 18 Flapping Micro 13
Information Processing 17 Mimetic Peptide 13
finding a much greater proportion of conference papers
than the other databases,presumably related to different
publishing strategies in engineering and computer science
compared with other disciplines.Overall,the top five journals
were (table 1):Biomaterials (Elsevier),Bioinspiration and
Biomimetics (IOP),Journal of Biomedical Materials Research
A (Wiley),Langmuir (ACS) and Acta Biomateriala (Elsevier).
The top six conferences were (table 2):ROBIO,SPIE,ICAL,
EMBC,ICRA and IROS.Of these,ROBIO dominated the
publication numbers,comprising more than one-third of the
conference output.
Second,how rapidly is biomimetics expanding as a
subject?From a relatively small field of tens of papers
in the mid-1990s,biomimetics has exponentially expanded
thereafter to nowreach nearly 3000 papers per year (figure 4).
The subject area has doubled in size every 2–3 years,far
outstripping the modest expansion of about 6% per year for
science in general (Larsen and von Ins 2010).Based on this
finding,there is a boom in bioinspired research,with leading
discoveries in biomimetics laying the foundations for large
areas of present and future research.As these developments
in robotics and engineering are translated into technology,
they have the potential for significant societal and economic
impacts.This growth of technological transfer is also seen in
the rapid rise of patents granted in biomimetics (Bonser 2006,
Bonser and Vincent 2007),indicating that a rapid development
of new technologies derived from biological models is taking
place.
Third,what subjects does biomimetics encompass?The
results of this analysis are displayedina wordcloudof frequent
terms in biomimetic research (figure 5).As expected,the
word biomimetic is the most popular word.Then,perhaps
more revealingly,other leading terms are ‘robot’ and ‘control’,
which suggests that a main thrust of biomimetic research is to
take inspiration from how animals control their bodies and
sensory systems for application to robotics.Other concepts
from the word cloud indicate a wide variety of research
in biomimetics,including the taxonomy and abilities of
biological organisms,terms from biomedical research and
bioengineering,and concepts from computer science and
artificial intelligence.
Finally,are there distinct research communities within
biomimetics?This question was addressed with techniques
fromnetwork theory applied to a graph of frequent biomimetic
topics linked given by common pairings within the titles of
papers.Terms that are strongly connected can then be pulled
together on the graph,while disparate topics are pushed apart
(figure 6).Applying a modularity analysis to this network
showed that the field of biomimetics was well connected
and may thus be considered a single discipline.Underlying
this inter-connectivity was a community structure into five
identifiable research themes:robotics and control,ethology-
based robotics,biomimetic actuators,biomaterials science and
structural bioengineering.
9.Conclusions
Biomimetics is a research field that is achieving particular
prominence through a wide variety of new discoveries in
biology and engineering.By applying an information analysis
to a comprehensive database of publications on biomimetics
over the last 15 years,we answered a set of strategic questions
about the past,present and future of the research field.The
most notable result was that there has been a rapid expansion
9
Bioinspir.Biomim.8 (2013) 013001 Perspective
of publications on biomimetics fromthe mid-1990s to present
day,doubling every 2–3 years to now reach a mature field
of nearly 3000 papers per year.Furthermore,the field is
still expanding,and so more growth can be expected.The
second main result was that there are a number of distinct
themes into which biomimetics can be partitioned,which we
identified as robotics and control,ethology-based robotics,
biomimetic actuators,and biomaterials science and structural
bioengineering.Taken together,these findings indicate that
biomimetics is becoming a dominant paradigm for robotics,
materials science and other technological disciplines,with
the potential for significant scientific,societal and economic
impact over this decade and into the future.
Acknowledgments
The authors thank the anonymous referees and are grateful for
discussions with G Indiveri,S Vassanelli,A Mura,M Evans
and other researchers fromthe Active Touch Laboratory at the
University of Sheffield and the Synthetic Perceptive,Emotive
and Cognitive Systems Laboratory at the Universitat Pompei
Fabra.This workwas supportedbythe FP7coordinationaction
Convergent Science Network (ICT-248986).
Appendix A.Database construction
The IEEE Xplore database (http://ieeexplore.ieee.org) was
used as a source of papers on biomimetics published in
IEEE journals and conferences.The Thomson Reuters Web of
Knowledge database (http://apps.webofknowledge.com) and
Elsevier’s Scopus (http://scopus.com) were used for other
journals and conferences.The search within the Web of
knowledge was restricted to engineering,physics,biophysics,
robotics,computer science,mathematics and mathematical
computational biology,while the search within Scopus
was restricted to engineering,physics,computer science,
mathematics,neurosciences and the decision sciences.These
terms restricted the type of biomimetics that we consider to
that published in engineering and related sciences.We did
consider using other search terms within areas of biology,
but our experience was that this resulted in many papers on
just pure biology without any clear relation to engineering or
technology.A range of synonyms for biomimetics were used
as search terms,including biomimetics,biomimetic,bionics,
bionic,biomimicry,bioinspired and bioinspiration.The search
engines in the three databases matched the terms with stored
metadata for each document,including the title,publication
title,abstract and author-defined keywords for each published
paper.
Since the information analysis was carried out in
MATLAB (Mathworks,MA),it was necessary to first convert
the results of the search to a readable document in a non-
propriety format.This was achieved in two steps.First,
the search results were exported to Endnote referencing
software (Thomson Reuters,NY).By default,Endnote stores
a bibliographic database in a propriety format.However,it
does give an option to save this database in extensible markup
language (XML),a human readable text-based format that is
closely related to hypertext markup language (HTML) used
for web pages.
A separate XML database was saved for each of the
biomimetic search terms given above.These were then
accessible fromMATLABby loading the text file into a single
alphanumeric string.Within XML,the content of the metadata
pertaining to each publication is enclosed within standardized
tabs.Hence,we could use standard text-matching commands
within MATLAB to extract the metadata of relevance to the
information analysis.Finally,before applying the information
analysis,this database of metadata was pre-processed to
eliminate repeated entries fromoverlapping search terms.
Appendix B.Database analysis
The metadata from the database of research articles in
biomimetics (appendix A) were then analyzed using a variety
of methods.
An initial analysis considered the biomimetic publications
by year and journal or conference in which they were
published.The results were plotted in figures 2–4 and
displayed in tables 1 and 2,as described in the main text
of this work.
The next analysis was to survey biomimetic publications
by topic,which was estimated fromcounting the most frequent
terms occurring in titles of papers.One complicating factor
is that the most common terms are just words that occur
generally in titles,such as parts of speech including ‘of’,
‘for’ and ‘a’.After experimenting with various methods,we
found the most reliable way to remove these was to construct
a list of these non-informative terms,and then remove them
fromthe database entries to leave concepts that are informative
about the field of biomimetics.These were presented in a word
cloud by exporting the list of words and their frequencies to
an appropriate web-based tool (wordel;http://wordel.com),
which was then manipulated into an appropriate graphical
format.
Our final analysis was to split these topics into overall
themes,judged from research terms that occur commonly
together.Asuitable co-occurrence measure for a pair of words
is the frequency that the words occur together in the title
population (number of co-occurrences per number of titles)
normalized by the product of the frequencies of the individual
words in the pair:
c(word
A
,word
B
) =
f (word
A
,word
B
)
f (word
A
) f (word
B
)
.(B.1)
If the words were independent and randomly distributed,then
the co-occurrence measure should equal 1;meanwhile,values
of c less than or greater than 1 indicate words occurring
together less than or greater than chance,respectively.This co-
occurrence measure can then be used to find overall research
themes by application of modularity analysis to determine
community structure.Co-occurrences between pairs of words
define links between nodes (the words) on an undirected
graph,with link strength given by the co-occurrence measure.
The network-analysis software Gephi (http://gephi.org) was
then used to display the links graphically with related words
‘pulled’ together by the Force Atlas algorithm (figure 6).
10
Bioinspir.Biomim.8 (2013) 013001 Perspective
We used standard Modularity and Force Atlas tools within
the Gephi software,which are described more fully in the
software’s documentation (Bastian et al 2009).
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